1. Field of the Invention
This invention relates to a nitride semiconductor and a method for manufacturing the same.
2. Background Art
Nitride semiconductors including GaN find wide application in light emitting diodes for display and illumination, semiconductor lasers for the next generation DVD (digital versatile disk), and electronic devices.
The nitride semiconductor crystal has a hexagonal wurtzite structure, which has no symmetry along the c-axis. Hence, an epitaxial film grown on the c-surface has front-rear polarity, that is, a group III surface and a group V surface. The surface of a GaN single crystal substrate may have nonuniformity in crystal polarity and surface orientation. Use of such a substrate is likely to cause within-wafer variation in crystal growth rate and impurity doping.
JP-A-2007-157765(Kokai) discloses a technique related to a gallium nitride semiconductor light emitting device with the crystal growth surface being a nitrogen-polar surface. In this technique, the direction of electric field at the p-side GaN/AlGaN interface is reversed to attract holes toward the light emitting region, thereby avoiding carrier depletion at the interface.
However, this technique is not sufficient to control crystal polarity in the wafer surface.